1. Field of the Invention
The present invention relates to an image display apparatus and a method of driving the same. Also, the present invention, for example, can be applied to an electronic still camera having an active matrix type image display portion using an organic Electro Luminescence (EL) element. Also, the present invention makes it possible to reduce power consumption as compared with the existing case by stopping the control for a write transistor made in accordance with a write signal when there is no change in image data.
2. Description of the Related Art
Heretofore, an electronic still camera, a video camera or the like functions as an image display apparatus to enhance a usability for a user. That is to say, the electronic still camera acquires moving image data from an image pickup element, and displays an image corresponding to the moving image data thus acquired on an image display portion. As a result, the electronic still camera makes it possible to confirm an object of image-capturing based on the moving image, thereby enhancing the usability for the user.
In addition, when a shutter button is manipulated by the user, the electronic still camera temporarily holds image data obtained from the image pickup element in a memory, and acquires the image-capturing results based on a still image. The electronic still camera displays an image corresponding to the image data temporarily held in the memory on the image display portion. As a result, the electronic still camera makes it possible to confirm the image-capturing results right after the photographing, thereby enhancing the usability for the user.
In recent years, with regard to this sort of image display apparatus, an active matrix type image display apparatus using an organic EL element has been actively developed. Here, the image display apparatus using the organic EL element is an image display apparatus utilizing a luminous phenomenon of an organic thin film which emits a light by applying thereto an electric field. The organic EL element can be driven by applying thereto a voltage of 10 V or less. Therefore, in this sort of image display device, the power consumption can be reduced. In addition, the organic EL element is a self light emitting element. Therefore, in this sort of image display apparatus, the weight saving and the thinning can be carried out because no backlight device is demanded. Moreover, the organic EL element has the feature that its response speed is high, that is, about several microseconds. Therefore, this sort of image display apparatus has the feature that a residual image is hardly generated in a phase of display of the moving image.
Specifically, in the active matrix type image display apparatus using the organic EL element, pixel circuits each composed of an organic EL element and a drive circuit for driving the organic EL element are disposed in a matrix, thereby forming a display portion. In the image display apparatus, a signal line drive circuit and a scanning line drive circuit are disposed in the circumference of the display portion. The signal line drive circuit drives the pixel circuits in accordance with image data successively inputted thereto through respective signal lines provided in the display portion. Also, the scanning line drive circuit drives the pixel circuits through respective scanning lines provided in the display portion.
Heretofore, with regard to the image display apparatus using the organic EL element, a method of configuring a pixel circuit using two transistors is disclosed in Japanese Patent Laid-Open No. 2007-310311 (hereinafter referred to as Patent Document 1). Therefore, according to the method disclosed in Patent Document 1, the configuration can be simplified. In addition, Patent Document 1 discloses a circuit configuration with which there are corrected the dispersion of threshold voltages, and the dispersion of mobilities in drive transistors for driving the respective organic EL elements. Therefore, according to the circuit configuration disclosed in Patent Document 1, it is possible to prevent image quality from being deteriorated due to the dispersion of the threshold voltages, and the dispersion of the mobilities in the drive transistors.
In addition, Japanese Patent Laid-Open No. 2007-133284 (hereinafter referred to as Patent Document 2) proposes a circuit configuration with which processing for correcting the dispersion of the threshold voltages of the drive transistors is exerted in multiple batches. According to the circuit configuration disclosed in Patent Document 2, even when a time allocated to gradation setting for a pixel circuit is shortened due to high precision promotion, the sufficient time can be allocated to the correction for the dispersion of the threshold voltages. Therefore, even in the case of the high precision promotion, it is possible to prevent the deterioration of the image quality due to the dispersion of the threshold voltages.